High powered lasers which provide secondary output beams at a different wavelength than the fundamental beam at which the laser lases have been made. For example, second, third and fourth harmonic intracavity lasers have been provided. See for example U.S. Pat. No. 5,898,717. The use of harmonic lasers or optical parametric oscillators enables a wide range of wavelengths to be supplied by reliable lasers such as the Nd:YAG, Nd:YLF or Nd:YVO4. See U.S. Pat. No. 6,108,356. In the case of the third and fourth harmonic lasers, powerful UV lasers can be provided. However, many applications require a variable power output, particularly for UV lasers. Thus, the user at one time will require a certain power and will also desire to adjust the laser to another lower or higher power. It is particularly desired to control the pulse energy of a harmonic laser.
Numerous patents are directed to controlling fundamental beam output. For example, U.S. Pat. No. 5,197,074 (Emmons) discloses a laser that it is capable of generating a laser output having preserved mode quality, waste position and output divergence as well as a selectable amplitude within a relative range of amplitudes and a selectable duration. Another example of a fundamental laser output control is shown by U.S. Pat. No. 5,339,323 (Hunter). This patent discloses the control of the laser pulse by a high loss time duration control signal supplied to a Q-switch. There is still a need in the art for lasers which produce variable power secondary output beams.
Lasers have been used in biological analysis using a matrix assisted laser desorption and ionization technique. See U.S. Pat. No. RE37,485. Such technique is useful in the biotech industry as it allows rather accurate analysis of the presence of biological components. In such systems, a matrix is added to the biological sample. The matrix absorbs UV laser energy typically a wavelength of from about 325 nm to 375 nm. A pulsed UV laser beam is used to ionize the biological sample mixed with the matrix which absorbs energy at approximately 325 nm to 375 nm. The ionized sample is then analyzed in a mass spectrometer. Depending on the type of sample or the component sought or both, different amounts of energy need to be supplied to the matrix to obtain optimal results.
Generally, in the prior art, nitrogen lasers which lase at 337 nm have been used. Nitrogen lasers are gas lasers. They are difficult to maintain and have a short useful life. The power of the nitrogen laser beam is controlled by using an attenuator which can be rotated to provide the desired power to a biological sample. Such a device is not desirable because the attenuator is mechanically operated and can have a significant time lag. Moreover, mechanical parts are unreliable and slow in response compared to a solid state device.